The present invention relates generally to a process and product for lubricating metal, and more particularly to such a process and product used prior to cold forming of the metal.
Chemical lubricant compositions span a broad range covering metal working fluids and coolants, of both oil, and oil in water emulsions and water base "synthetic" mixtures, as well as heavy oils, powders, pastes and greases, which all perform the lubricant functions of reducing contact friction, transferring heat, and allowing a physical or mechanical operation to take place.
"Cold forming" of metal generally entails various work operations at room temperature such as extrusion of metal backward or forward; drawing; ironing; forming; and the like. For example, a metal wire may be drawn to a specific diameter through a die, or metal tubing to a specific wall thickness and diameter over a mandrel, or a metal shape may be formed through a press or heading machine. Each of these operations requires a continual reporting or lubricating layer having good "slip" characteristics, ie. no metal to metal contact, between the tooling and the work piece. The chemical and physical characteristics of this reporting layer determine the feasibility of the extrusion, as well as the tool life.
Presently, the majority of metal parts (such as steel parts) to be cold drawn are prepared with a zinc phosphate coating, chemically reacted with a buffered sodium stearate lubricant, while in other situations, a zinc phosphate coating is coupled with a combined inorganic or organic lubricant referred to as nonreactive soap coating. For more severe extrusions, the zinc phosphate coated stock may be tumbled with molybdenum disulfide. This metal preparation generally includes the following steps: alkaline cleaning; a hot water rinse; a sulfuric acid pickle; a cold water rinse; a hot water rinse; a zinc phosphate application; a cold water rinse; an alkaline neutralizer; and an application of a reactive organic soap lubricant.
In the steel industry, unlike a layer of paint or oil on the steel surface, the zinc phosphate layer is a conversion coating, which reacts with the base steel and utilizes a portion of it into the coating itself. The resulting precipitation is a mixture of iron from the steel with zinc and phosphate from the phosphate solution which forms zinc-iron phosphate crystals that are chemically bonded to the steel surface. This crystal pattern builds uniformly across the steel surface during immersion in the zinc phosphate bath until the characteristic sparkling grey coating covers the surface. The phosphate coating does not inherently provide lubricity, but it does provide a non-metallic barrier between the steel being extruded and the tools performing the deformation. Although this barrier role is important, the greater function of the zinc phosphate is to retain and react with subsequent carriers and lubricants. These subsequent layers are important for providing relief at critical points of reduction and cold drawing when tools and dies need to allow the passing metal surface to flow freely and smoothly.
The steps involved in the coating deposition are pickling, acceleration, coating and sludge. These steps are repeated each time a clean steel piece enters the solution. After these steps, the steel surface has an anchored crystalline structure thereon which serves two purposes for lubrication. The first purpose is "retention" of lime or stearate soaps, either applied in the pickle/process line or as a dry box lubricant prior to drawing. This is accomplished simply by the physical "sponge" nature of the crystal lattice, which is able to hold large quantities of inorganic lime and/or organic soaps. For some subsequent forming operations, the sheer quantity of retained soap will be the basis for the success of the operation. In other instances, the composition of the retained soap will play the key role. In still other applications, both quantity and composition will be influential. The second purpose is the chemical "reaction" with sodium and calcium stearate soaps. The stearate compounds, via a reactive soap tank or from within a dry box soap, displace the phosphate chemically connected to the zinc and bond directly to the zinc site. This bonded zinc stearate possesses a wide plastic range and high melting point necessary for difficult extrusions.
Current alternatives to the zinc phosphate procedure are oil replacements which are untidy, costly and environmentally unsound, as well as being of only limited effectiveness. In fact, the zinc phosphate procedure itself contains a high concentration of soluble zinc which requires profuse rinsing and subsequent waste water treating and hazardous disposal. Further, a lesser percentage of soluble nickel normally is incorporated into zinc phosphate mixtures, which faces even greater effluent restrictions. Still further, a natural and inevitable byproduct of the zinc process involves the generation of an insoluble, zinc bearing sludge in the process tank itself, which requires periodic solution decants and additional hazardous waste disposal. Yet another drawback lies in the fact that all of the solutions used in the zinc phosphate procedure have a relatively short lifespan in reference to square footage of metal processed and/or weeks of productivity. Desludging and discarding of solutions impede production, add costly labor time to the process, and contribute greatly to waste treatment costs and permanent hazardous disposal sites.
Thus, it is an object of the present invention to provide a process and product for lubricating metal prior to cold forming of the metal which is as, if not more effective than current zinc phosphate treatments, while being more efficient and more environmentally sound. Further, it is an object of the present invention to provide such a process and product which does not require profuse rinsing and subsequent waste water treating and hazardous disposal. Still further, it is an object of the present invention to provide such a process and product which does not require periodic solution decants and additional hazardous waste disposal of sludge. Yet still further, it is an object of the present invention to provide such a process and product which has a relatively long lifespan in reference to square footage of metal processed and/or weeks of productivity.